This invention relates generally to torque measuring apparatus and more particularly, it relates to an improved torque measurement circuit and method for an internal combustion engine of the four cylinder, two-cycle type which cancels an error created by inertia impulse force due to the mass of the pistons and connecting rods.
The need for monitoring and control systems for automotive vehicles has arisen due to recent enactment of stringent laws relating to exhaust pollution-control and safety standards. In order to insure, for example, less exhaust pollution, there is required a more effective and efficient operation of an internal combustion engine. This, in turn, leads to the necessity of monitoring of a number of performance characteristics during the normal operating conditions of an automotive vehicle. Torque measurement is one of the more significant parameters, if it is not the most critical. Thus, accurate measurement of torque must be achieved so that the quantity can be properly correlated to regulate other performance characteristics such as ignition timing, fuel mixture control, transmission control and pollution-emission control.
In U.S. Pat. No. 3,693,426 to Donald R. Little issued on Sept. 26, 1972 and entitled "Portable Useful Horsepower Measuring Instrument", there is disclosed an apparatus for measuring horsepower by detecting and producing a first signal directly proportional to engine RPM or vehicle speed and a second signal directly proportional to an absolute acceleration parallel to the roadway grade. From these two parameters, a resultant signal is calculated to be representative to the useful horsepower and torque.
U.S. Pat. No. 3,729,989 to Donald R. Little issued on May 1, 1973, is quite similar to his earlier U.S. Pat. No. 3,693,426 and further discloses a transducer strain gauge which delivers an analog d.c. signal directly proportional to the force experienced thereon due to the torque produced by a prime mover. A multiplier circuit receives a first input signal directly proportional to the velocity of the prime mover and a second signal being the said analog force signal so as to determine the useful horsepower.
U.S. Pat. No. 3,817,092 to Karl Ludloff issued on June 18, 1974, teaches a method of measuring torque and power of a rotating element in a system by determining angular velocity and angular acceleration at a particular point in time. U.S. Pat. No. 3,921,446 to Karl Ludloff issued on Nov. 25, 1975 represents an improvement over his earlier U.S. Pat. No. 3,817,092 patent and embodies a general purpose torque meter and dynanometer system which includes a computer for receiving a plurality of independent measurements from sensors to detect relevant engine operating parameters such as engine speed, throttle position, engine and air temperatures, and brake-fluid pressure. Thus, this system will be more accurate than his earlier apparatus, which only allowed for a single subtraction for external load losses and internal system losses, due to the fact that the latter system takes into account an average of many measurements for determining torque and/or power.
In U.S. Pat. No. 4,098,242 to George H. Anderson issued July 4, 1978, there is taught an automatic control system which includes a switching circuit for changing the gain of the system in accordance with load conditions of a prime mover such as an internal combustion engine.
In U.S. Pat. No. 4,344,140 to Chun-Keung Leung issued on Aug. 10, 1982, there is disclosed a closed loop engine roughness control for controlling the fuel delivery to an internal combustion engine to maintain the operation of the engine at a predetermined roughness level. The roughness control includes a roughness sensor to detect the instantaneous rotational velocity of the engine's crankshaft to generate an engine roughness signal. This engine roughness signal is multiplied by an engine speed signal to generate a speed corrected roughness signal. The speed corrected roughness signal is summed with a reference signal to produce a bias signal operative to modify the fuel delivery signals generated by a fuel controlled computer. These fuel signals as modified by the bias signal control the fuel delivery to the engine, thereby maintaining the operation of the engine at the predetermined roughness level.
W. B. Ribbens, from the University of Michigan, investigated the use of an inexpensive, non-contacting sensor for the measurement of the quasi-average torque of an internal combustion engine. His method of torque measurement utilizes an inexpensive sensor for directly measuring instantaneous crankshaft angular velocity and relatively simple electronic signal processing to generate a signal proportional to instantaneous crankshaft angular acceleration. The result of Mr. Ribbens' experimental study showing that the desired torque is highly correlated with the relative transformation of crankshaft acceleration is published in S. A. E. Technical Paper Ser. No. 810155 entitled "A Non-Contacting Torque Sensor for the Internal Combustion Engine."
Heretofore, the prior art attempts discussed above measure the torque being transmitted through a rotating shaft by estimating an engine variable which is related to torque such as cylinder instantaneous pressure, manifold pressure, and engine position. However, none of them take into consideration the effect of torque impulses or inertia forces due to the mass of the pistons and connecting rods.
Accordingly, it would be desirable to provide an improved torque measurement circuit and method for an internal combustion engine of the four cylinder, two-cycle type which cancels an error created by inertia impulse force due to the mass of the pistons and connecting rods. The present invention produces an electrical voltage signal directly proportional to torque which is the sum of first and second signals both representative of the pressures inside the cylinders exerting a force on the pistons and of the inertia force due to the mass of the pistons and connecting rods. These two signal components are obtained by means of synchronous detection circuits driven at twice the rotational velocity of the crankshaft of the engine.